Data synchronization

ABSTRACT

One or more techniques and/or computing devices are provided for data synchronization. For example, an in-flight log may be maintained to track storage operations that are received by a first storage node, but have not been committed to both first storage of the first storage node and second storage of a second storage node that has a replication relationship, such as a disaster recovery relationship, with the first storage node. A dirty region log may be maintained to track regions within the first storage that have been modified by storage operations that have not been replicated to the second storage. Accordingly, a catchup synchronization phase (e.g., asynchronous replication by a resync scanner) may be performed to replicate storage operations (e.g., replicate data within dirty regions of the first storage that were modified by such storage operations) to the second storage until the first storage and the second storage are synchronized.

RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S.application Ser. No. 14/865,442, filed on Sep. 25, 2015, now allowed,titled “DATA SYNCHRONIZATION,” which is incorporated herein byreference.

BACKGROUND

Many storage networks may implement data replication for data lossprotection. For example, a first storage cluster may comprise a firststorage node configured to provide clients with primary access to datastored within a first storage device and/or other storage devices. Asecond storage cluster may comprise a second storage node configured toprovide clients with access to data stored within a second storagedevice (e.g., failover access to replicated data within the secondstorage device) and/or other storage devices (e.g., primary access todata stored within a third storage device). The first storage node andthe second storage node may be configured according to a disasterrecovery relationship, such that the second storage node may providefailover access to replicated data that was replicated from the firststorage device to the second storage device.

When the first storage node and the second storage node are in asynchronous replication state, storage operations (e.g., data changefileops, offload fileops, metadata change fileops, abort operations,etc.) are synchronously replicated from the first storage node and firststorage device to the second storage node and the second storage device.For example, a write storage operation may be received from a client bythe first storage node. Before a response is provided back to the clientthat the write storage operation is complete, the write storageoperation is to be both written to the first storage device andreplicated to the second storage device. If a replication error or otherissue occurs (e.g., the second storage node has a failure or reboots, anetwork connection between the first storage node and the second storagenode is lost, etc.), then the first storage node and the second storagenode may transition into an out-of-sync state without strict dataconsistency between the first storage device and the second storagedevice.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a component block diagram illustrating an example clusterednetwork in accordance with one or more of the provisions set forthherein.

FIG. 2 is a component block diagram illustrating an example data storagesystem in accordance with one or more of the provisions set forthherein.

FIG. 3 is a flow chart illustrating an exemplary method of datasynchronization.

FIG. 4A is a component block diagram illustrating an exemplary computingdevice for data synchronization, where a first storage node and a secondstorage node are implementing synchronous replication.

FIG. 4B is a component block diagram illustrating an exemplary computingdevice for data synchronization, where network communication between afirst storage node and a second storage node is lost.

FIG. 4C is a component block diagram illustrating an exemplary computingdevice for data synchronization, where a first storage node processes afourth storage operation while network communication is lost between thefirst storage node and a second storage node.

FIG. 4D is a component block diagram illustrating an exemplary computingdevice for data synchronization, where a first storage node processes afifth storage operation while network communication is lost between thefirst storage node and a second storage node.

FIG. 4E is a component block diagram illustrating an exemplary computingdevice for data synchronization, where network communication between afirst storage node and a second storage node is restored.

FIG. 4F is a component block diagram illustrating an exemplary computingdevice for data synchronization, where catchup synchronization isperformed between a first storage node and a second storage node.

FIG. 4G is a component block diagram illustrating an exemplary computingdevice for data synchronization, where a sixth storage operation issynchronously committed to first storage and replicated to secondstorage while a first storage node and a second storage node areout-of-sync.

FIG. 4H is a component block diagram illustrating an exemplary computingdevice for data synchronization, where a sixth storage operation issynchronously committed to first storage and replicated to secondstorage while a first storage node and a second storage node areout-of-sync.

FIG. 4I is a component block diagram illustrating an exemplary computingdevice for data synchronization, where catchup synchronization isperformed between a first storage node and a second storage node.

FIG. 5 is a component block diagram illustrating an exemplary computingdevice for maintaining data consistency between snapshots.

FIG. 6 is an example of a computer readable medium in accordance withone or more of the provisions set forth herein.

DETAILED DESCRIPTION

Some examples of the claimed subject matter are now described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the following description,for purposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

One or more techniques and/or computing devices for data synchronizationare provided. For example, an in-flight log may be maintained to trackstorage operations that are received by a first storage node, but havenot been committed to both first storage of the first storage node andsecond storage of a second storage node having a replicationrelationship, such as a disaster recovery relationship, with the firststorage node. In an example, a storage operation may be implemented towrite to the first storage by the first storage node simultaneously withthe creation of an entry, within the in-flight log, for the storageoperation (e.g., the first storage and the in-flight log may be changesimultaneously through shared write access provided by a file system).

A dirty region log, such as a bitmap, may be used to track what regionsof the first storage have been changed by storage operations that havenot yet been replicated to the second storage. In this way, a catchupsynchronization phase may be performed using the in-flight log and/orthe dirty region log to replicate (e.g., asynchronous replication by aresync scanner) storage operations (e.g., dirty regions modified bystorage operations) to the second storage and second storage node. Async log, corresponding to the in-flight log and/or the dirty regionlog, may be efficiently maintained and used to reduce latency forresponding to clients (e.g., a storage operation may be written to thefirst storage and a notification of the storage operation being completemay be sent to the client notwithstanding the storage operation not yetbeing replicated to the second storage because data of the storageoperation will later be asynchronously replicated based upon the synclog), maintain low overhead (e.g., the sync log may comprise bitmapsthat may be efficiently zeroed out), maintain consistency with snapshots(e.g., the sync log may be used to identify a snapshot differencebetween a snapshot of the first storage and of the second storage),provide persistent storage (e.g., the sync log may be stored on disk),etc.

To provide context for data synchronization, FIG. 1 illustrates anembodiment of a clustered network environment 100 or a network storageenvironment. It may be appreciated, however, that the techniques, etc.described herein may be implemented within the clustered networkenvironment 100, a non-cluster network environment, and/or a variety ofother computing environments, such as a desktop computing environment.That is, the instant disclosure, including the scope of the appendedclaims, is not meant to be limited to the examples provided herein. Itwill be appreciated that where the same or similar components, elements,features, items, modules, etc. are illustrated in later figures but werepreviously discussed with regard to prior figures, that a similar (e.g.,redundant) discussion of the same may be omitted when describing thesubsequent figures (e.g., for purposes of simplicity and ease ofunderstanding).

FIG. 1 is a block diagram illustrating an example clustered networkenvironment 100 that may implement at least some embodiments of thetechniques and/or systems described herein. The example environment 100comprises data storage systems or storage sites 102 and 104 that arecoupled over a cluster fabric 106, such as a computing network embodiedas a private Infiniband, Fibre Channel (FC), or Ethernet networkfacilitating communication between the storage systems 102 and 104 (andone or more modules, component, etc. therein, such as, nodes 116 and118, for example). It will be appreciated that while two data storagesystems 102 and 104 and two nodes 116 and 118 are illustrated in FIG. 1,that any suitable number of such components is contemplated. In anexample, nodes 116, 118 comprise storage controllers (e.g., node 116 maycomprise a primary or local storage controller and node 118 may comprisea secondary or remote storage controller) that provide client devices,such as host devices 108, 110, with access to data stored within datastorage devices 128, 130. Similarly, unless specifically providedotherwise herein, the same is true for other modules, elements,features, items, etc. referenced herein and/or illustrated in theaccompanying drawings. That is, a particular number of components,modules, elements, features, items, etc. disclosed herein is not meantto be interpreted in a limiting manner.

It will be further appreciated that clustered networks are not limitedto any particular geographic areas and can be clustered locally and/orremotely. Thus, in one embodiment a clustered network can be distributedover a plurality of storage systems and/or nodes located in a pluralityof geographic locations; while in another embodiment a clustered networkcan include data storage systems (e.g., 102, 104) residing in a samegeographic location (e.g., in a single onsite rack of data storagedevices).

In the illustrated example, one or more host devices 108, 110 which maycomprise, for example, client devices, personal computers (PCs),computing devices used for storage (e.g., storage servers), and othercomputers or peripheral devices (e.g., printers), are coupled to therespective data storage systems 102, 104 by storage network connections112, 114. Network connection may comprise a local area network (LAN) orwide area network (WAN), for example, that utilizes Network AttachedStorage (NAS) protocols, such as a Common Internet File System (CIFS)protocol or a Network File System (NFS) protocol to exchange datapackets. Illustratively, the host devices 108, 110 may begeneral-purpose computers running applications, and may interact withthe data storage systems 102, 104 using a client/server model forexchange of information. That is, the host device may request data fromthe data storage system (e.g., data on a storage device managed by anetwork storage control configured to process I/O commands issued by thehost device for the storage device), and the data storage system mayreturn results of the request to the host device via one or more networkconnections 112, 114.

The nodes 116, 118 on clustered data storage systems 102, 104 cancomprise network or host nodes that are interconnected as a cluster toprovide data storage and management services, such as to an enterprisehaving remote locations, cloud storage (e.g., a storage endpoint may bestored within a data cloud), etc., for example. Such a node in a datastorage and management network cluster environment 100 can be a deviceattached to the network as a connection point, redistribution point orcommunication endpoint, for example. A node may be capable of sending,receiving, and/or forwarding information over a network communicationschannel, and could comprise any device that meets any or all of thesecriteria. One example of a node may be a data storage and managementserver attached to a network, where the server can comprise a generalpurpose computer or a computing device particularly configured tooperate as a server in a data storage and management system.

In an example, a first cluster of nodes such as the nodes 116, 118(e.g., a first set of storage controllers configured to provide accessto a first storage aggregate comprising a first logical grouping of oneor more storage devices) may be located on a first storage site. Asecond cluster of nodes, not illustrated, may be located at a secondstorage site (e.g., a second set of storage controllers configured toprovide access to a second storage aggregate comprising a second logicalgrouping of one or more storage devices). The first cluster of nodes andthe second cluster of nodes may be configured according to a disasterrecovery configuration where a surviving cluster of nodes providesswitchover access to storage devices of a disaster cluster of nodes inthe event a disaster occurs at a disaster storage site comprising thedisaster cluster of nodes (e.g., the first cluster of nodes providesclient devices with switchover data access to storage devices of thesecond storage aggregate in the event a disaster occurs at the secondstorage site).

As illustrated in the exemplary environment 100, nodes 116, 118 cancomprise various functional components that coordinate to providedistributed storage architecture for the cluster. For example, the nodescan comprise a network module 120, 122 and a data module 124, 126.Network modules 120, 122 can be configured to allow the nodes 116, 118(e.g., network storage controllers) to connect with host devices 108,110 over the network connections 112, 114, for example, allowing thehost devices 108, 110 to access data stored in the distributed storagesystem. Further, the network modules 120, 122 can provide connectionswith one or more other components through the cluster fabric 106. Forexample, in FIG. 1, a first network module 120 of first node 116 canaccess a second data storage device 130 by sending a request through asecond data module 126 of a second node 118.

Data modules 124, 126 can be configured to connect one or more datastorage devices 128, 130, such as disks or arrays of disks, flashmemory, or some other form of data storage, to the nodes 116, 118. Thenodes 116, 118 can be interconnected by the cluster fabric 106, forexample, allowing respective nodes in the cluster to access data on datastorage devices 128, 130 connected to different nodes in the cluster.Often, data modules 124, 126 communicate with the data storage devices128, 130 according to a network file system (NFS) protocol a storagearea network (SAN) protocol, such as Small Computer System Interface(SCSI) or Fiber Channel Protocol (FCP), for example. Thus, as seen froman operating system on a node 116, 118, the data storage devices 128,130 can appear as locally attached to the operating system. In thismanner, different nodes 116, 118, etc. may access data blocks throughthe operating system, rather than expressly requesting abstract files.

It should be appreciated that, while the example embodiment 100illustrates an equal number of network and data modules, otherembodiments may comprise a differing number of these modules. Forexample, there may be a plurality of network and data modulesinterconnected in a cluster that does not have a one-to-onecorrespondence between the network and data modules. That is, differentnodes can have a different number of network and data modules, and thesame node can have a different number of network modules than datamodules.

Further, a host device 108, 110 can be networked with the nodes 116, 118in the cluster, over the networking connections 112, 114. As an example,respective host devices 108, 110 that are networked to a cluster mayrequest services (e.g., exchanging of information in the form of datapackets) of a node 116, 118 in the cluster, and the node 116, 118 canreturn results of the requested services to the host devices 108, 110.In one embodiment, the host devices 108, 110 can exchange informationwith the network modules 120, 122 residing in the nodes (e.g., networkhosts) 116, 118 in the data storage systems 102, 104.

In one embodiment, the data storage devices 128, 130 comprise volumes132, which is an implementation of storage of information onto diskdrives or disk arrays or other storage (e.g., flash) as a file-systemfor data, for example. Volumes can span a portion of a disk, acollection of disks, or portions of disks, for example, and typicallydefine an overall logical arrangement of file storage on disk space inthe storage system. In one embodiment a volume can comprise stored dataas one or more files that reside in a hierarchical directory structurewithin the volume.

Volumes are typically configured in formats that may be associated withparticular storage systems, and respective volume formats typicallycomprise features that provide functionality to the volumes, such asproviding an ability for volumes to form clusters. For example, where afirst storage system may utilize a first format for their volumes, asecond storage system may utilize a second format for their volumes.

In the example environment 100, the host devices 108, 110 can utilizethe data storage systems 102, 104 to store and retrieve data from thevolumes 132. In this embodiment, for example, the host device 108 cansend data packets to the network module 120 in the node 116 within datastorage system 102. The node 116 can forward the data to the datastorage device 128 using the data module 124, where the data storagedevice 128 comprises volume 132A. In this way, in this example, the hostdevice can access the storage volume 132A, to store and/or retrievedata, using the data storage system 102 connected by the networkconnection 112. Further, in this embodiment, the host device 110 canexchange data with the network module 122 in the host 118 within thedata storage system 104 (e.g., which may be remote from the data storagesystem 102). The host 118 can forward the data to the data storagedevice 130 using the data module 126, thereby accessing volume 1328associated with the data storage device 130.

It may be appreciated that data synchronization may be implementedwithin the clustered network environment 100. In an example, storageoperations, associated with data within the data storage device 128 ofthe node 116, may be replicated to the data storage device 130 of thenode 118. For example, a catchup synchronization phase may use anin-flight log and/or a dirty region log (e.g., used to track storageoperations received by the node 116 and/or regions within the datastorage device 128 modified by storage operations but not yet replicatedto the data storage device 130) to asynchronously replicate data to thedata storage device 130. It may be appreciated that data replication maybe implemented for and/or between any type of computing environment, andmay be transferrable between physical devices (e.g., node 116, node 118,etc.) and/or a cloud computing environment (e.g., remote to theclustered network environment 100).

FIG. 2 is an illustrative example of a data storage system 200 (e.g.,102, 104 in FIG. 1), providing further detail of an embodiment ofcomponents that may implement one or more of the techniques and/orsystems described herein. The example data storage system 200 comprisesa node 202 (e.g., host nodes 116, 118 in FIG. 1), and a data storagedevice 234 (e.g., data storage devices 128, 130 in FIG. 1). The node 202may be a general purpose computer, for example, or some other computingdevice particularly configured to operate as a storage server. A hostdevice 205 (e.g., 108, 110 in FIG. 1) can be connected to the node 202over a network 216, for example, to provides access to files and/orother data stored on the data storage device 234. In an example, thenode 202 comprises a storage controller that provides client devices,such as the host device 205, with access to data stored within datastorage device 234.

The data storage device 234 can comprise mass storage devices, such asdisks 224, 226, 228 of a disk array 218, 220, 222. It will beappreciated that the techniques and systems, described herein, are notlimited by the example embodiment. For example, disks 224, 226, 228 maycomprise any type of mass storage devices, including but not limited tomagnetic disk drives, flash memory, and any other similar media adaptedto store information, including, for example, data (D) and/or parity (P)information.

The node 202 comprises one or more processors 204, a memory 206, anetwork adapter 210, a cluster access adapter 212, and a storage adapter214 interconnected by a system bus 242. The storage system 200 alsoincludes an operating system 208 installed in the memory 206 of the node202 that can, for example, implement a Redundant Array of Independent(or Inexpensive) Disks (RAID) optimization technique to optimize areconstruction process of data of a failed disk in an array.

The operating system 208 can also manage communications for the datastorage system, and communications between other data storage systemsthat may be in a clustered network, such as attached to a cluster fabric215 (e.g., 106 in FIG. 1). Thus, the node 202, such as a network storagecontroller, can respond to host device requests to manage data on thedata storage device 234 (e.g., or additional clustered devices) inaccordance with these host device requests. The operating system 208 canoften establish one or more file systems on the data storage system 200,where a file system can include software code and data structures thatimplement a persistent hierarchical namespace of files and directories,for example. As an example, when a new data storage device (not shown)is added to a clustered network system, the operating system 208 isinformed where, in an existing directory tree, new files associated withthe new data storage device are to be stored. This is often referred toas “mounting” a file system.

In the example data storage system 200, memory 206 can include storagelocations that are addressable by the processors 204 and adapters 210,212, 214 for storing related software application code and datastructures. The processors 204 and adapters 210, 212, 214 may, forexample, include processing elements and/or logic circuitry configuredto execute the software code and manipulate the data structures. Theoperating system 208, portions of which are typically resident in thememory 206 and executed by the processing elements, functionallyorganizes the storage system by, among other things, invoking storageoperations in support of a file service implemented by the storagesystem. It will be apparent to those skilled in the art that otherprocessing and memory mechanisms, including various computer readablemedia, may be used for storing and/or executing application instructionspertaining to the techniques described herein. For example, theoperating system can also utilize one or more control files (not shown)to aid in the provisioning of virtual machines.

The network adapter 210 includes the mechanical, electrical andsignaling circuitry needed to connect the data storage system 200 to ahost device 205 over a computer network 216, which may comprise, amongother things, a point-to-point connection or a shared medium, such as alocal area network. The host device 205 (e.g., 108, 110 of FIG. 1) maybe a general-purpose computer configured to execute applications. Asdescribed above, the host device 205 may interact with the data storagesystem 200 in accordance with a client/host model of informationdelivery.

The storage adapter 214 cooperates with the operating system 208executing on the node 202 to access information requested by the hostdevice 205 (e.g., access data on a storage device managed by a networkstorage controller). The information may be stored on any type ofattached array of writeable media such as magnetic disk drives, flashmemory, and/or any other similar media adapted to store information. Inthe example data storage system 200, the information can be stored indata blocks on the disks 224, 226, 228. The storage adapter 214 caninclude input/output (I/O) interface circuitry that couples to the disksover an I/O interconnect arrangement, such as a storage area network(SAN) protocol (e.g., Small Computer System Interface (SCSI), iSCSI,hyperSCSI, Fiber Channel Protocol (FCP), a network file system (NFS)protocol, etc.). The information is retrieved by the storage adapter 214and, if necessary, processed by the one or more processors 204 (or thestorage adapter 214 itself) prior to being forwarded over the system bus242 to the network adapter 210 (and/or the cluster access adapter 212 ifsending to another node in the cluster) where the information isformatted into a data packet and returned to the host device 205 overthe network connection 216 (and/or returned to another node attached tothe cluster over the cluster fabric 215).

In one embodiment, storage of information on arrays 218, 220, 222 can beimplemented as one or more storage “volumes” 230, 232 that are comprisedof a cluster of disks 224, 226, 228 defining an overall logicalarrangement of disk space. The disks 224, 226, 228 that comprise one ormore volumes are typically organized as one or more groups of RAIDs. Asan example, volume 230 comprises an aggregate of disk arrays 218 and220, which comprise the cluster of disks 224 and 226.

In one embodiment, to facilitate access to disks 224, 226, 228, theoperating system 208 may implement a file system (e.g., write anywherefile system) that logically organizes the information as a hierarchicalstructure of directories and files on the disks. In this embodiment,respective files may be implemented as a set of disk blocks configuredto store information, whereas directories may be implemented asspecially formatted files in which information about other files anddirectories are stored.

Whatever the underlying physical configuration within this data storagesystem 200, data can be stored as files within physical and/or virtualvolumes, which can be associated with respective volume identifiers,such as file system identifiers (FSIDs), which can be 32-bits in lengthin one example.

A physical volume corresponds to at least a portion of physical storagedevices whose address, addressable space, location, etc. doesn't change,such as at least some of one or more data storage devices 234 (e.g., aRedundant Array of Independent (or Inexpensive) Disks (RAID system)).Typically the location of the physical volume doesn't change in that the(range of) address(es) used to access it generally remains constant.

A virtual volume, in contrast, is stored over an aggregate of disparateportions of different physical storage devices. The virtual volume maybe a collection of different available portions of different physicalstorage device locations, such as some available space from each of thedisks 224, 226, and/or 228. It will be appreciated that since a virtualvolume is not “tied” to any one particular storage device, a virtualvolume can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, a virtual volume can include one or more logical unit numbers(LUNs) 238, directories 236, Qtrees 235, and files 240. Among otherthings, these features, but more particularly LUNS, allow the disparatememory locations within which data is stored to be identified, forexample, and grouped as data storage unit. As such, the LUNs 238 may becharacterized as constituting a virtual disk or drive upon which datawithin the virtual volume is stored within the aggregate. For example,LUNs are often referred to as virtual drives, such that they emulate ahard drive from a general purpose computer, while they actually comprisedata blocks stored in various parts of a volume.

In one embodiment, one or more data storage devices 234 can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumesstored on a data storage device, a target address on the data storagedevice can be used to identify one or more LUNs 238. Thus, for example,when the node 202 connects to a volume 230, 232 through the storageadapter 214, a connection between the node 202 and the one or more LUNs238 underlying the volume is created.

In one embodiment, respective target addresses can identify multipleLUNs, such that a target address can represent multiple volumes. The I/Ointerface, which can be implemented as circuitry and/or software in thestorage adapter 214 or as executable code residing in memory 206 andexecuted by the processors 204, for example, can connect to volume 230by using one or more addresses that identify the LUNs 238.

It may be appreciated that data synchronization may be implemented forthe data storage system 200. In an example, storage operations,associated with data within the data storage devices 234 of the node202, may be replicated to a second data storage device of a second node.For example, a catchup synchronization phase may use an in-flight logand/or a dirty region log (e.g., used to track storage operationsreceived by the node 202 and/or regions within the data storage devices234 modified by storage operations not yet replicated to the second datastorage device) to asynchronously replicate data to the second datastorage device. It may be appreciated that data synchronization may beimplemented for and/or between any type of computing environment, andmay be transferrable between physical devices (e.g., node 202, host 205,etc.) and/or a cloud computing environment (e.g., remote to the node 202and/or the host 205).

One embodiment of data synchronization is illustrated by an exemplarymethod 300 of FIG. 3. A first storage node may be configured to provideclients with access to data stored within first storage. A secondstorage node may be configured to provide clients with access to datastored within second storage or other storage. The first storage nodeand the second storage node may be configured according to a disasterrecovery relationship. For example, data from the first storage may bereplicated to the second storage so that the second storage node mayprovide clients with failover access to replicated data within thesecond storage in the event the first storage node fails. While in asynchronous state, a storage operation, received by the first storagenode from a client, may be synchronously stored within the first storageand replicated to the second storage before a storage operation completeresponse is provided back to the client (e.g., a storage operation maybe split into two storage operations that may be committed to the firststorage and the second storage in any order or in parallel). In anexample, an in-flight log, used to track storage operations received bythe first storage node but not yet committed to both the first storageand the second storage, may be maintained (e.g., a storage operation maybe implemented to simultaneously write to the first storage and createan entry within the in-flight log). In an example, the in-flight log maybe maintained as an in-core version (e.g., stored within memory), andmay be persisted to an in-flight metadata file within a file system(e.g., persistent onto disk for surviving a failure).

However, synchronous replication may be impractical under certainsituations, such as where the second storage node fails or reboots,communication from the first storage node to the second storage node islost, a relatively high network latency, etc. At 302, the first storageof the first storage node and the second storage of the second storagenode may be determined as having transitioned into an out-of-sync state(e.g., an inability to synchronously commit storage operations to thefirst storage and replicate to the second storage before responding backto clients within an acceptable time frame).

While in the out-of-sync state, a dirty region log may be used to trackstorage operations to the first storage that are committed by the firststorage node but are not committed by the second storage node forreplication (e.g., storage operations, received while communication tothe second storage node is unavailable, that are committed by the firststorage node and indicated as complete to clients notwithstanding notbeing replicated to the second storage), at 304. In an example, while inthe out-of-sync state, if a size of a file grows beyond a thresholdsize, then a size of the file at a time of transitioning into theout-of-sync state may be captured so that subsequent changes beyond thatsize are not tracked and thus anything beyond that size is implicitlydirty. In an example, the dirty region log may be persisted to disk,such as to a private inode space of a volume or a metadata file of afile system of the first storage node. In an example, the dirty regionlog may be maintained as a bitmap comprising bitmap entriescorresponding to regions within the first storage. When a storageoperation is committed by the first storage node to modify a region, abit of a corresponding bitmap entry may be modified (e.g., changed froma “1” to a “0” or from a “0” to a “1”) to indicate that the region isnow a dirty region that has been modified and thus is not consistentwith a corresponding region within the second storage because thestorage operation (e.g., the dirty region) has not yet been replicatedto the second storage. In this way, the dirty region log may beevaluated to identify dirty regions, modified by storage operations, notyet replicated from the first storage to the second storage. In anexample, various versions of the dirty region may be maintained as a setof dirty region logs. A current version of the dirty region log may beeither rolled forward to a new version or rolled back to an olderversion.

At 306, a catchup synchronization phase (e.g., asynchronous replicationof storage operations not yet committed to the second storage may beperformed after communication to the second storage node becomesavailable; dirty regions within the first storage may be replicated tothe second storage; etc.) may be performed to synchronize storageoperations, designated as being associated with dirty regions of thefirst storage by the dirty region log, from the first storage to thesecond storage (e.g., replication of the dirty regions to correspondingregions within the second storage). In an example, the dirty region logand/or the in-flight log may be evaluated to determine whether toreplicate a region of the first storage to the second storage. Forexample, catchup synchronization functionality (e.g., asynchronousreplication) may be used to replicate a region based upon at least oneof the dirty region log indicating that the region is dirty (e.g., hasbeen modified by a storage operation that has not been replicated to thesecond storage) or the in-flight log indicating that a storageoperation, associated with the region, has not been committed to boththe first storage and the second storage. In an example, a resyncscanner may be invoked to evaluate the dirty region log and/or thein-flight log to identify one or more regions within the first storageto replicate to the second storage using catchup synchronizationfunctionality. Responsive to synchronizing a region, specified as dirtyby a dirty region entry within the dirty region log, as committed to thesecond storage, the dirty region entry may be cleared.

During the catchup synchronization phase, new storage operations may bereceived and processed by the first storage node. If a new storageoperation corresponds to a dirty region identified by the dirty regionlog, then the first storage operation may be committed to the dirtyregion within the first storage (e.g., and an operation completeresponse may be provided back to a client that issued the new storageoperation) for subsequent synchronization by catchup synchronizationfunctionality (e.g., asynchronous replication by the resync scanner). Ifthe new storage operation corresponds to a non-dirty region within thefirst storage, then the new storage operation may be synchronously, suchas in real-time, committed to the first storage and replicated to thesecond storage (e.g., and an operation complete response may be providedback to a client that issued the new storage operation and the newstorage operation is committed to both the first storage and the secondstorage).

In an example, the dirty region log and/or the in-flight log may be usedto reconcile snapshots. For example, a first snapshot of the firststorage may be generated. A second snapshot of the second storage may begenerated, such as while the storage nodes are in the out-of-sync state,and thus the second snapshot may be different than the first snapshotbecause one or more storage operations may have been committed to thefirst storage but not the second storage. In an example, storageoperation processing may be facilitated during the generation of thefirst snapshot and/or the second snapshot (e.g., snapshots may begenerated without draining storage operations, thus reducing latencyincreases otherwise caused by draining storage operations). The dirtyregion log and/or the in-flight log may be used to identify a snapshotdifference between the first snapshot and the second snapshot. Thesecond snapshot may be modified based upon the snapshot difference tocreate a reconciled snapshot having a data consistency with the firstsnapshot. In this way, the dirty region log and/or the in-flight log maybe used to track data consistency between the first storage and thesecond storage for replication and/or snapshots.

FIGS. 4A-4I illustrate examples of a computing device comprising asystem 400 for data synchronization. FIG. 4A illustrates a first storagenode 402 configured to provide clients with access to data stored withinfirst storage 404 (e.g., local storage locally attached to the firststorage node 404, network storage communicatively coupled to the firststorage node 404 over a network, etc.) and/or other storage notillustrated. A second storage node 412 is configured to provide clientsto access to data stored within second storage 414 (e.g., provideclients with failover access to replicated data within the secondstorage 414) and/or other storage not illustrated (e.g., provide clientswith primary access to data within third storage). In an example, thesecond storage 414 may be used to store replicated data that isreplicated, such as synchronously replicated 416 over a network 410,from the first storage 404 to the second storage 414. For example, afirst region comprising data (A), a second region that is empty, a thirdregion that is empty, a fourth region comprising data (B), a fifthregion comprising data (C), and/or other regions of the first storage404 may be replicated to the second storage 414 as replicated regions.In this way, the first storage 404 and the second storage 414 may be ina synchronized state.

An in-flight log 406 may be maintained for the first storage node 402.The in-flight log 406 may track storage operations that are received bythe first storage node 402, but are not yet committed by both the firststorage node 402 to the first storage 404 and the second storage node412 to the second storage 414. For example, a first storage operationand a second storage operation may have been received by the firststorage node 402, and thus a first entry for the first storage operationand a second entry for the second storage operation may have beencreated in the in-flight log 406 to indicate that the first storageoperation and the second storage operation have not yet been committedto both the first storage 404 and the second storage 414. Accordingly,once the first storage node 402 commits the first storage operation andthe second storage operation to the first storage 404 and thesynchronous replication 416 replicates the first storage operation andthe second storage operation to the second storage node 412 that thencommits the first storage operation and the second storage operation tothe second storage 414, the first entry and the second entry may bemodified (e.g., removed, zeroed out, etc.) to indicate that the storageoperations have been synchronously committed to the first storage 404and the second storage 414. Thus, the first storage node 402 may providestorage operation complete notifications to clients that sent thestorage operations. In an example, a third storage operation may bereceived by the first storage node 402, and a third entry may be created(e.g., set to “1”) within the in-flight log 406 to indicate that thethird storage operation has not been committed to both the first storage404 and the second storage 414.

FIG. 4B illustrates the first storage node 402 and the second storagenode 412 committing the third storage operation. Accordingly, the thirdentry within the in-flight log 406 may be modified (e.g., removed,zeroed out, etc.), thus indicating that the third storage operation hasbeen synchronized between the first storage 404 and the second storage414. Subsequently, a communication loss 422, over the network 410,between the first storage node 402 and the second storage node 412 mayoccur. Thus, the synchronous replication 416, over the network 410, maybe lost and the first storage 404 and the second storage 414 may becomeout-of-sync due to the first storage node 402 processing storageoperations that are unable to be adequately replicated to the secondstorage node 412 and second storage 414.

FIG. 4C illustrates the first storage node 402 and the second storagenode 412 transitioning into an out-of-sync state, where the firststorage 404 is out-of-sync with the second storage 414 (e.g., a loss ofdata consistency because storage operations may be processed andresponded back to clients as complete by the first storage node 402without synchronous replication to the second storage node 412). Forexample, a client may send a forth storage operation 430 to the firststorage node 402 for writing data (D) into the third region 432 of thefirst storage 404. A fourth entry, not illustrated, may be createdwithin the in-flight log 406 to indicate that the fourth storageoperation 430 was received by the first storage node 402, but has notbeen committed to both the first storage 404 and the second storage 414.A bit, of a third dirty region entry 434, within the dirty region log408, associated with the third region 432, may be set to indicate thatthe third region 432 of the first storage 404 has been modified (e.g.,set to 1 to indicate that the third region 432 has been made dirty withthe data (D) of the fourth storage operation 430). In this way, thirddirty region entry 434 of the dirty region log 408 indicates that thethird region 432 of the first storage 404 is out-of-sync and/orinconsistent with a corresponding third region 433 within the secondstorage 414.

FIG. 4D illustrates the first storage node 402 and the second storagenode 412 in the out-of-sync state. In an example, a second client maysend a fifth storage operation 440 to the first storage node 402 forwriting data (E) into the second region 442 of the first storage 404. Afifth entry, not illustrated, may be created within the in-flight log406 to indicate that the fifth storage operation 440 was received by thefirst storage node 402, but has not been committed to both the firststorage 404 and the second storage 414. A bit, of a second dirty regionentry 444, of the dirty region log 408, associated with the secondregion 442, may be set to indicate that the second region 442 of thefirst storage 404 has been modified (e.g., set to 1 to indicate that thesecond region 442 has been made dirty with the data (E) of the fifthstorage operation 440). In this way, second dirty region entry 444 ofthe dirty region log 408 indicates that the second region 442 of thefirst storage 404 is out-of-sync and/or inconsistent with acorresponding third region 435 within the second storage 414.

FIG. 4E illustrates communication being reestablished over the network410 between the first storage node 402 and the second storage node 412.FIG. 4F illustrates the first storage node 402 and the first storage 404being out-of-sync with the second storage node 412 and the secondstorage 414 after the communication has been reestablished, and thus acatchup synchronization phase may be performed, such as asynchronousreplication by a resync scanner, to synchronize storage operations, suchas the fourth storage operation 430 (e.g., replication of data (D)written to the third region 432 by the fourth storage operation 430) andthe fifth storage operation 440 (e.g., replication of data (E) writtento the second region 443 by the fifth storage operation 440), based uponthe in-flight log 406 and/or the dirty region log 408. For example,catchup synchronization 450 of the data (D) within the third region 432of the first storage 404 may be performed to asynchronously replicatethe data (D), written by the fourth storage operation 430 to the thirdregion 432, into the corresponding third region 433 within the secondstorage 414 of the second storage node 412 as replicated data (D) 452based upon at least one of the in-flight log 406 indicating that thefourth storage operation 430 was received by the first storage node 402and has not been committed to both the first storage 404 and the secondstorage 412 or the third dirty region entry 434 of the dirty region log408 indicating that the third region 432 of the first storage 404 isout-of-sync and/or inconsistent with the corresponding third region 433within the second storage 414. Once the third region 432 of the firststorage 404 has been replicated to the second storage 414, the bit ofthe third dirty region entry 434 may be modified (e.g., removed, zeroedout, etc.) to indicate that the third region 432 is no longer dirty andthus is data consistent with the corresponding third region 433 of thesecond storage 414.

FIG. 4G illustrates the first storage node 402 receiving a sixth storageoperation 460 from a third client. The sixth storage operation 460 maywrite data (F) into a sixth region 462 of the first storage 404. Becausethe dirty region log indicates that the sixth region 462 is a non-dirtyregion, the sixth storage operation 460 may be synchronously committedby the first storage node 402 to the first storage 404 by writing thedata (F) into the sixth region 462 and replicating (e.g., real-timesynchronization 466) to the second storage 414 such as into acorresponding sixth region 467 as replicated data (F) 468, asillustrated by FIG. 4H. In an example where a storage operationcorresponds to a dirty region, such as the second region 442, thestorage operation may be committed into the first storage 404 and may belater synchronized to the second storage 414 by a resync scanner becausethe second region 442 is already indicated as being dirty by the dirtyregion log 408.

FIG. 4I illustrates catchup synchronization 470 of the data (E) withinthe second region 442 of the first storage 404 being performed toasynchronously replicate the data (E), written by the fifth storageoperation 440 to the second region 442, into the corresponding secondregion 435 within the second storage 414 of the second storage node 412as replicated data (E) 472 based upon at least one of the in-flight log406 indicating that the fifth storage operation 440 was received by thefirst storage node 402 and has not been committed to both the firststorage 404 and the second storage 412 or the second dirty region entry444 of the dirty region log 408 indicating that the second region 442 ofthe first storage 404 is out-of-sync and/or inconsistent with thecorresponding second region 435 within the second storage 414. Once thesecond region 442 of the first storage 404 has been replicated to thesecond storage 414, the bit of the second dirty region entry 444 may bemodified (e.g., removed, zeroed out, etc.) to indicate that the secondregion 442 is no longer dirty and thus is data consistent with thecorresponding second region 435 of the second storage 414.

FIG. 5 illustrates an example of a system 500 for snapshotreconciliation. A first storage node 502 may be associated with firststorage 504 that is out-of-sync with second storage 512 of a secondstorage node 510 having a disaster recovery relationship with the firststorage node 502. An in-flight log 506 and/or a dirty region log 508 maybe maintained for the first storage node 502 to indicate what storageoperations have not been committed to both the first storage 504 and thesecond storage 512 and/or to indicate what regions within the firststorage 504 are dirty because data within such regions have not beenreplicated to the second storage 512.

While the first storage 504 and the second storage 512 are out-of-sync,a first snapshot 514 of the first storage 504 and a second snapshot 516of the second storage 512 may be generated. The in-flight log 506 and/orthe dirty region log 508 may be used to compare 518 the first snapshot514 and the second snapshot 516 to identify a snapshot difference 520between the first snapshot 514 and the second snapshot 516. The snapshotdifference 502 may correspond to data within the first storage 504 thatis not data consistent with the second storage 512, such as due tostorage operation that were committed to the first storage 504 but notyet replicated to the second storage 512 while the first storage node502 and the second storage node 510 are in an out-of-sync state.Accordingly, the second snapshot 516 may be modified based upon thesnapshot difference 520 to create a reconciled snapshot 522 that hasdata consistency with the first snapshot 514.

Still another embodiment involves a computer-readable medium comprisingprocessor-executable instructions configured to implement one or more ofthe techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 6, wherein the implementation 600comprises a computer-readable medium 608, such as a CD-ft DVD-R, flashdrive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 606. This computer-readable data 606, such asbinary data comprising at least one of a zero or a one, in turncomprises a set of computer instructions 604 configured to operateaccording to one or more of the principles set forth herein. In someembodiments, the processor-executable computer instructions 604 areconfigured to perform a method 602, such as at least some of theexemplary method 300 of FIG. 3, for example. In some embodiments, theprocessor-executable instructions 604 are configured to implement asystem, such as at least some of the exemplary system 400 of FIGS. 4A-4Iand/or at least some of the exemplary system 500 of FIG. 5, for example.Many such computer-readable media are contemplated to operate inaccordance with the techniques presented herein.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), EEPROM and/or flash memory, CD-ROMs, CD-Rs, CD-RWs, DVDs,cassettes, magnetic tape, magnetic disk storage, optical or non-opticaldata storage devices and/or any other medium which can be used to storedata.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A method comprising: generating a first snapshotof first storage and a second snapshot of second storage; utilizing alog to identify a snapshot difference between the first snapshot and thesecond snapshot; and modifying the second snapshot using the snapshotdifference to create a reconciled snapshot having data consistency withthe first snapshot.
 2. The method of claim 1, wherein the first snapshotand the second snapshot are generated when the first storage and thesecond storage are out-of-sync.
 3. The method of claim 1, comprising:processing storage operations during the generation of the firstsnapshot.
 4. The method of claim 1, comprising: processing storageoperations during the generation of the second snapshot.
 5. The methodof claim 1, wherein the log comprises an in-flight log used to trackpending operations.
 6. The method of claim 1, wherein the log comprisesa dirty region log used to track dirty data within the first storage notyet replicated to the second storage.
 7. The method of claim 1, whereinthe snapshot difference corresponds to changes made to the first storagebut not the second storage while the first storage and the secondstorage are out-of-sync.
 8. A non-transitory machine readable mediumhaving stored thereon machine executable code, which when executed by amachine, causes the machine to: generate a first snapshot of firststorage and a second snapshot of second storage; utilize a log toidentify a snapshot difference between the first snapshot and the secondsnapshot; and modify the second snapshot using the snapshot differenceto create a reconciled snapshot having data consistency with the firstsnapshot.
 9. The non-transitory machine readable medium of claim 8,wherein the first snapshot and the second snapshot are generated whenthe first storage and the second storage are out-of-sync.
 10. Thenon-transitory machine readable medium of claim 8, wherein the machineexecutable code causes the machine to: process storage operations duringthe generation of the first snapshot.
 11. The non-transitory machinereadable medium of claim 8, wherein the machine executable code causesthe machine to: process storage operations during the generation of thesecond snapshot.
 12. The non-transitory machine readable medium of claim8, wherein the log comprises an in-flight log used to track pendingoperations.
 13. The non-transitory machine readable medium of claim 8,wherein the log comprises a dirty region log used to track dirty datawithin the first storage not yet replicated to the second storage. 14.The non-transitory machine readable medium of claim 8, wherein thesnapshot difference corresponds to changes made to the first storage butnot the second storage while the first storage and the second storageare out-of-sync.
 15. A computing device comprising: a memory comprisingmachine executable code for performing a method; and a processor coupledto the memory, the processor configured to execute the machineexecutable code to cause the processor to: generate a first snapshot offirst storage and a second snapshot of second storage; utilize a log toidentify a snapshot difference between the first snapshot and the secondsnapshot; and modify the second snapshot using the snapshot differenceto create a reconciled snapshot having data consistency with the firstsnapshot.
 16. The computing device of claim 15, wherein the firstsnapshot and the second snapshot are generated when the first storageand the second storage are out-of-sync.
 17. The computing device ofclaim 15, wherein the machine executable code causes the processor to:process storage operations during the generation of the first snapshot.18. The computing device of claim 15, wherein the machine executablecode causes the processor to: process storage operations during thegeneration of the second snapshot.
 19. The computing device of claim 15,wherein the log comprises an in-flight log used to track pendingoperations.
 20. The computing device of claim 15, wherein the logcomprises a dirty region log used to track dirty data within the firststorage not yet replicated to the second storage.